The present invention relates to an electrical connector or socket for electrically connecting the terminal pins of a circuit package to an LSI (large scale integrated) circuit, a printed circuit board and the like, and in particular to an electrical connector which can connect or disconnect the circuitry by moving parts or members of the connector or socket in the direction normal to the axis thereof.
A conventional connector of the above-mentioned type is schematically shown in FIG. 9, which depicts the case where an LSI circuit 2 is connected to a printed circuit board 1. A plurality of socket contacts 3 is embraced in a housing or base insulator 4. A cover insulator 6 is slidably combined with the base insulator 4. In the cover insulator 6, there is formed a plurality of penetrating guide holes 5. When a pin contact 7 of the LSI 2 is inserted into the corresponding guide hole 5, and the LSI circuit 2 is then moved in the direction of an arrow 8 together with the cover insulator 6, the pin contact 7 is brought into contact with the corresponding socket contact 3. More specifically, the pin contact 7 is brought into contact with the socket contact 3 as illustrated in FIG. 10. The pin contact 7 is in a laterally slidable manner inserted between a pair of resilient contact portions 9 extending from the socket contact 3 in the direction of the arrow 8 as illustrated in FIG. 10. As a result, the contact portions 9 are spread and slidably make press-contact with a peripheral surface of the pin contact 7.
FIG. 11 shows a graph in the case where the pin contact 7 is inserted between the pair of confronting contact portions 9 of the socket contact 3 and removed therefrom, with the insertion force and removal force plotted as ordinate and the lateral movement of the contact pin 7 as abscissa. In FIG. 11, since the directions of the insertion force and removal force are opposite to each other, the respective directions are shown by a positive direction and a negative direction in the graph. As can be seen from FIG. 11, a maximum value F.sub.P of the insertion force is greater than the removal force F.sub.N, more specifically the maximum insertion force F.sub.P is approximately twice the removal force F.sub.N. Furthermore, when the frictional force of the contact portions 9 and the contact pin 7 is P and the coefficient of friction between the pin contact 7 and the socket contact 3 is .mu., F.sub.N =2 .mu.P. As a result, a large force is required for laterally inserting the pin contact 7 between the pair of contact portions 9 of the socket contact 3. Therefore, when a large number of socket contacts 3 are provided in this type of electrical connector, the insertion and removal operation is difficult.
Furthermore, as shown in FIG. 12, the initial fitting space g between the opposing contact portions 9 of the socket contact 3 must be smaller than the diameter of the pin contact 7. On the other hand, there must be an appropriate inner protrusion h on each of the contact portions 9 in order that the pin contact 7 can be smoothly laterally inserted between the contact portions 9 of the socket contact 3. In other words, the initial outer diameter W.sub.1 of the contact portions 9 of the socket contact 3 must be larger than the diameter t of the contact pin 7. As a result, when the pin contact 7 is inserted into the socket contact 3, the outer diameter of the socket contact 3 is increased to W.sub.2. Therefore, it is difficult to position a number of the socket contacts 3 with high density.
In the case where the socket contacts 3 are positioned with high density, the displacement (t-g)/2 of each resilient contact portion 9, which is equal to d/2, becomes extremely small, because the fitting space g between the contact portions 9 cannot be excessively reduced as can be seen from the above. Therefore, in order to obtain stable frictional force, the socket 3 must be fabricated by from a very hard spring, that is, a spring having a large spring constant. Therefore, if there is a fabrication error in the diameter of the pin contact 7 or a positional error thereof, the frictional force between the contact surfaces 9 and the contact pin 7 becomes insufficient for obtaining stable contact therebetween. In such a case, other problems occur. For example, the socket contact 3 may be excessively displaced so that excessive frictional force is caused between the contact surfaces 9 and the contact pin 7, and the resilient contact portions 9 are permanently deformed, or extremely large insertion and removal forces are required.
These problems occur not only in the case where the LSI circuit 2 is connected to the printed circuit board 1 as explained above, but also in the case where printed circuit boards are connected to each other.